The needs of a rider participating in a mountain biking trek or race will sometimes change during the ride. During a climb, the rider is ascending a trail with great exertion; a helmet providing unobstructed breathing, ventilation and comfort is desirable. During a descent, the rider needs greater protection as they speed downhill. Conventional helmets have struggled to handle both scenarios well. Conventional helmets with chin bars are built to provide protection to downhill riders, but are not ideal for ascending. The chin bar may obstruct ventilation and breathing, and the added protection increases the weight of the helmet on the wearer's head. Furthermore, a conventional helmet that would be comfortable during a climb may not provide sufficient protection against the high-speed impacts that can happen during a descent. Conventional helmets leave riders with a choice between the inconvenience of carrying two helmets on a ride, an uncomfortable climb, or a dangerous descent.